If you mean that you want to install the steel ball to tow trailers...I do have some experience installing them under a W124...hitch...is that how it is called???
In europe we have hitches for the W124 that exist of a steel bar that needs to be mounted under the car/under the absolute rear of the trunk floor. This bar goes from the right chassis beam to the left chassis beam and holds the steel ball to tow the trailer.
This steel bar is mounted to steel support angles that are installed in the chassis beams inside the trunk of the car. These steel support angles are mounted with steel contra plates near the rear axle.
On each side of the trunk near the rear fender/quarter panels, we have more support steel that is mounted near the hinges of the trunk lid and the taillights. These support steel bars are diagonal mounted and will be visible after all the trunk panels/upholstery is brought back to place again.
You need to remove the rear bumper, trunk upholstery panels and spare wheel. You need to drill all the holes yourself (besides the ones for the upper side of the diagonals near the trunk lid hinges) and you need to install all parts before tightening the bolts...
I do not know where to but a hitch in the states...
with a minor 600+k